1. Field of the Invention
This invention relates generally to sample testing products and techniques, and more specifically to an improved solid phase extraction (SPE) filtration disk and a method for its manufacture.
2. Description of the Prior Art
Within the environmental testing arena laboratories are faced with a multitude of sample testing methods and techniques for the analysis of drinking water, waste water, and hazardous waste. These testing methods are typically approved and compiled with Environmental Protection Agency (EPA) documents, and serve as a basis by which the laboratory can determine the appropriate test method for detecting the presence and concentration of various compounds of interest. With regards to these test methods, technological advances are frequently achieved prior to and in conjunction with the revision of such published methods, thereby allowing for a laboratory to take advantage of the "best available technology" (BAT).
The recent advances in the field of Solid Phase Extraction (SPE) technology has allowed for laboratories to perform certain extraction methods in a safer, more economical, and a more time saving manner than previous standard methods. The information to follow will discuss a prior extraction method and current SPE technology.
Current methods for the extraction of pesticides, herbicides, and semi-volatile compounds from various matrices, (such as drinking water, waste water, or hazardous waste), call for the use of liquid/liquid extraction (L/L), in which a solvent is used that is relatively non-polar with respect to the compounds of interest. The solvent is mixed with the sample matrix and the compounds of interest form intermolecular interactions based on hydrogen bonding with the solvent. The solvent which now contains the compounds of interest is then removed from the sample matrix, concentrated, and analyzed via the appropriate analytical instrument. The most common problems faced by laboratories employing this method are with regards to excess analytical interference, low compound recoveries, the use of large volumes of solvents (typically chlorinated carcinogenic suspects), and lengthy extraction times (up to several hours per sample).
In response to these problems the EPA now allows for liquid/solid (L/S) extraction. Using SPE techniques, a sample matrix (specifically drinking water) is passed through a plastic column that is filled with one of several sorbent beds depending on the compounds of interest. The plastic column is attached to a vacuum from the bottom, and the sample matrix is drawn through the column. The compounds of interest are then absorbed onto the sorbent based on polar/non-polar interactions. A small volume of non-polar solvent (relative to the sorbent bed), is then passed through the column, thus removing the compounds of interest while leaving less desirable polar compounds in the sorbent. The eluent is then concentrated and analyzed by the appropriate analytical instrument. This method has been effective in reducing certain analytical interferences, solvent usage, and extraction time, however, it is not without its drawbacks. Typical problems encountered with the use of SPE columns are with respect to: specific analytical interferences due to the plastic columns (phthalate esters), low recoveries resulting from channeling effects under high vacuum that create a path of least resistance not allowing for adequate absorption of the compounds of interest, and column clogging due to high particulate laden matrices.
Current SPE technology addresses the problems described above by the employment of a SPE disk impregnated with a singular sorbent. The standard SPE disk is manufactured using a Teflon material to which a sorbent is incorporated. The principle of reversed phase SPE is employed to extract aqueous samples in the same manner as described above. The Teflon disk provides adequate compound recoveries, however, it is extremely susceptible to clogging by seemingly clean aqueous samples, requiring many hours of aspiration under high vacuum. Alternatively, another manufacturer has produced a SPE disk using glass fiber filter paper. It has been determined from scanning electron micrographs (SEM) that this product is produced by pouring sorbent material on top of a pre-made filter paper, and then aspirating the paper with vacuum to create a caked layer of sorbent on top of the paper. This particular product has been reported to leak, crack, and provide less than adequate compound recoveries.
Accordingly, it is an object of this invention to provide the laboratory industry with a more reliable, leak proof filtration disk that would maintain high flow rates with particulate laden aqueous samples, without compromising compound recovery.